1. Field of the Invention
This invention relates generally to electricity meters and methods for measuring apparent power consumption, and more particularly to a novel electricity meter and method that measures both active power and apparent power.
2. Description of the Background
Until recently, the cost of electric power has been based on the so-called integrated active power (the product of voltage across a branch of an AC circuit and the component of the electric current that is in phase with the voltage) supplied to a customer measured in kilowatt-hours. However, the capacity of an electrical power system, which dictates the capital investment of electric power utility must make in generators, transformers, etc. depends on the apparent power (product of RMS current and RMS voltage without consideration of the effects of phase angle) it must supply. Since the average power factor of a customer usually is less than unity due, for example, to the presence of large reactive loads, the active power will be less than the apparent power. Hence, active power based revenue from a consumer will not necessarily reflect the utility's investment in equipment to serve that customer.
Public Service Commissions in several states and in Canada accordingly have allowed the utilities either to impose a surcharge based on the mismatch between apparent power and active power, or bill the consumer entirely on the apparent power.
Heretofore, metering of apparent power has generally been achieved by monitoring line current and line voltage, and multiplying the RMS values of current and voltage electronically. If separate transformers are used to monitor the line current and line voltage, the cost of the meter increases. Hall effect transducers are relatively inexpensive and have been used by power utility companies to provide economical watt transducers. However, such Hall effect transducers were not considered to be versatile enough to be used in a watt-hour meter. Therefore, a substantial reduction in cost can be achieved if Hall effect transducers can be used to meter both active power and apparent power.